1. Field of the Invention
The present disclosure relates synchronous machines, and in particular wound field synchronous generator machines.
2. Description of Related Art
Hybrid vehicles utilize electrical power generation systems coupled to variable speed internal combustion engines for propulsion. Such propulsion systems require a highly regulated electrical power supply, typically provided by a wound field synchronous generator machine. The engine couples to the generator through a drivetrain that can include an optional gearbox with an interconnecting shaft. The shaft transmits mechanical energy from the engine through a shaft to rotate a rotating portion of the synchronous machine, thereby generating electricity. A conventional voltage regulator controls the generator to provide a constant output voltage.
The inertias associated with the prime mover and optional gearbox in combination with the mechanical compliance of the drivetrain and synchronous machine rotor, e.g. spring rates, create a distributed mechanical spring-mass system with torsional resonances. As the synchronous machine presents a near constant mechanical load to the drivetrain, the synchronous machine provides negative damping for frequencies within the synchronous machine voltage regulation bandwidth. However, the synchronous machine can be subject to large load transients at frequencies outside of the machine voltage regulation bandwidth. These can alter the mechanical loading on the drivetrain, induce undesirable torsional oscillations in the system, and under certain circumstances, cause mechanical failures in the system.
Similarly, periodic fuel combustion within the engine and the generally nonlinear engine geometry result in torque disturbances and crankshaft speed oscillations that transfer to the rotating part synchronous machine through the drivetrain. These are typically not compensated for with voltage regulation. Instead, conventional vehicle systems incorporate mechanical devices such as a flywheel coupled to the crankshaft to reduce pulsation in the rotational speed of the crankshaft. While generally satisfactory, this adds to vehicle weight and size and adversely affects vehicle efficiency.
Conventional synchronous machines for hybrid vehicles have generally been considered satisfactory for their intended purposes. However, there is a need in the art for systems and methods of damping torsional oscillation in such synchronous machines and vehicle drivetrains without size and weight penalties. There also remains a need in the art for systems and methods of damping torsional oscillation in synchronous machines that are easy to make and use. The present disclosure presents a solution to these needs.